The only game you need for Xbox is Morrowind: Game of the Year Edition, outside of that, all other purchases are just things to build a hard plastic pillow for Morrowind's box to rest on.
Suggestions for a nice firm feel.
Raw 2: Unless your a wrestling fanatic, skip it. I enjoy the hell outta this game, great custumization with the entrance, large roster, 4 player season (every game should do this), the list goes on and on. only downside is the wrestling itself, which feels kinda awkward, but you'll eventually get used to it. Oh, the ladder matches.... HATE!!
Deus Ex Invisible War: The basketball in this game, while not even noteworthy, is 10x better than any EA game.
Fable: Great atmosphere and a nice dessert for players of long RPG's.
Suffering: I have played through this game 3 times, it's extrmemly fun and moody.
KOTOR 1+2: Both great games, and perfect for D&D style fans w/o a computer good enough to run some of the classics.
Crimson Skies: While the single player can get annoying, what the hells up with the save system?? at least it has one, and a mediocre story to boot. The real fun is online, and given that 2 people per console can play at a time, there's really no beating it on XBL.
Kingdom Under Fire: IF you've ever liked Kessen or Dynasty Warriors, I'd say go pick this up immediately. Large battles, tons of upgrades, and some of the best music I've ever heard in a game.
Theif Deadly Shadows: Outside of Morrowind, I have probably wasted the most needless amount of hours on this game. The random stealing, stealth kills, dark setting, cool story, and fun gadgets to mess with earn this game a top spot in my library.